The invention relates to the field of internal combustion rotary engines, and more specifically, to such engines of the oscillatory, or scissor action, rotating type.
Throughout the history of human civilization we have striven to reduce the need to expend our muscular energy. Having first learned how to use the energy of water and wind, we went on to master the energy of steam and petrol and finally harnessed the nuclear energy. But in this uncontrolled strive for supremacy we have upset the delicate balance of nature. The depletion of non-renewable resources and total pollution of the environment are the two global problems that make it impossible for us to continue developing our industries extensively i.e. along the road that has already lead mankind into an environmental dead end.
The Public and Governments in the majority of the developed nations have already come to appreciate the serious impasse we are in. The problem however is that we have fallen hostages to the machines with which we have populated our Earth. Each automotive vehicle and nearly each mechanical gadget carries inside it a little demon that provides us with mechanical energy but claims in return non-renewable resources and pollutes our environment. The name of this demon is an internal combustion engine, or ICE.
Invented over a century ago, ICE has become an integral part of our lifestyle. In the course of its history ICE has undergone numerous modifications, all aimed at improving its two basic characteristics i.e. power rating and fuel economy. ICE's make use of different thermodynamic cycles, their components are differently arranged relative to one another, and numerous engineering solutions proliferate. They cover a broad spectrum of use from portable mechanical gadgets such as chain saws and hedge trimmers to huge locomotives and ocean going vessels. However the basic design of ICE is unchanged from what it was over a century ago and is still made up of two basic components: a piston reciprocally moving inside a cylinder and a drive mechanism based on the use of a crankshaft and connecting rods.
Medium and large sized ICE's have long been targeted by environmental criticism and their fuel economy has always been recognized as a quality important to the consumer. In past decades, this has driven the development of fuel efficient and environmentally friendly car engines based on the Diesel cycle and making use of a variety of state-of-the-art technologies. Large engineering companies throughout the world are constantly engaged in further improving their ICE's, the cost of such improvements being spread over the multi-billion revenues of the automotive, ship-building, transport and other industries. While improving the engine efficiency and reducing exhaust pollution, the incorporation of advanced electronic controls does not cause an unacceptable increase in the engine size or cost. This makes it possible for the ICE industry as a whole to follow its current path and look upon any design that does not fit the conventional reciprocal scheme as an interesting but non-essential technical curiosity.
The situation is quite different in the small ICE scene (typically up to 11 HP). The application spectrum for engines of this size is extremely broad and covers all sorts of hand-held and mobile gadgets such as chain-saws, hedge-trimmers and grass cutters, generators, compressors and pumps, motor bikes and scooters and so on. All such applications spell out similar requirements as follows:
High unit power PA0 Small size and light weight PA0 Simple operation and maintenance PA0 High reliability and robustness PA0 High toxicity of exhaust gases due to: PA0 High noise and vibration levels due to: PA0 High fuel consumption due to: PA0 Poor reliability and short service life due to: PA0 Lubrication other than through combustible mix (e.g. injection) to avoid burning lubricant PA0 Use of supercharging to improve scavenging PA0 Use of a valves to improve phasing PA0 Direct fuel injection to avoid using combustible mix for scavenging PA0 Use of electronic controls to improve combustion process PA0 Use of catalyst to clean the exhaust
This class of engines is also subjected to quite rigid price expectations (usually up to $100) as any unreasonable increase in price would shrink the potential market dramatically.
Up to recently this market had been dominated by the 2-stroke Otto cycle internal combustion engine with one or two cylinders, valveless, air cooled and lubricated by adding lubricant to the fuel. The indisputable advantage of this design is in its unique simplicity. The high unit power requirement is satisfied thanks to the 2-cycle operation, which means that twice the amount of fuel and air mix is pumped through the work volume. Fuel ignition in each cylinder occurs once per every revolution of the main shaft thus ensuring a more uniform rotation. This short list however exhausts the advantages of this design as all its other particulars fall under shortcomings, the principle of which are as follows:
Charring of lubricant that is burned with the combustible mix PA1 Use of combustible mix for cylinder scavenging PA1 Degraded combustion conditions due to presence of lubricant PA1 High intensity of exhaust PA1 Poorly balanced overall design PA1 Loss of combustible mix to scavenging PA1 Degraded combustion conditions due to presence of lubricant PA1 Highly aggressive exhaust gasses PA1 Intensive use of work volume PA1 High RPM to compensate for efficiency losses
The limited advantages of the 2-stroke Otto engine had up to a point outweighed its numerous shortcomings. Yet nowadays, with the generally increased environmental awareness causing a significant tightening up of environmental regulations throughout the industrialized nations, this engine type as we know it, may be outlawed. A vast industry has suddenly found itself searching for a technical solution that would enable it to cross the new barrier.
The traditional recipes for solving the problem would be one or some of the following:
All of the above solutions necessitate the installation of additional systems that would make the engine bulkier and costlier while depriving it of its cardinal advantage i.e. simplicity.
A radical solution would be to adopt the 4-stroke cycle that has been perfected by the automotive industry. But scaling down an 8-cylinder engine with 4 valves per cylinder and advanced electronic controls from 4 liters and 200 HP to a milk-pack sized engine developing under 10 HP is not a feasible engineering task. If it were, making and operating such an engine would involve unacceptable costs. Even the simple change from 2 to 4 strokes would bring about some considerable design overheads (valve system, lubrication system etc). It is also worth noting that a 4-stroke engine would exhibit lower unit power, less uniform rotation and lower maximum RPM than its 2-stroke counterpart.
The majority of known alternative power units such as external combustion engines, axial piston engines, small gas turbines, re-emerging updated 2-stroke Diesel engines and so on make a poor match to the requirements of low-end applications as summarized above. The high degree of their work volume fragmentation, the large number of auxiliary systems they require and the bulkiness of their drive mechanisms all make them an unsuitable solution for the task.
A suitable solution could be provided in the form of a rotary piston engine as such engines are distinguished by unit power that is sufficiently high to satisfy the application. Yet the majority of known arrangements of this type all have some drawbacks that prevent them from competing against the traditional reciprocal engine. Thus the well known Wankel rotary piston engine demonstrates poor fuel economy and "dirty" exhaust due to its falcate shape of the combustion chamber. Trying to scale it down is also bound to aggravate the apex seal problems typical of this engine to the extent of making it impracticable.
Another broadly promoted design is the so-called RandCam engine developed by Reg Technologies of Canada on the basis of U.S. Pat. No. 4,401,070 issued to McCann in 1983. While technically much superior to the Wankel engine, the RandCam engine does not readily lend itself to downsizing due to highly fragmented work volume and the way its sliding vanes are mounted and sealed. In fact these drawbacks are typical of any rotary piston engine utilizing sliding vanes.
Yet another popular rotary piston engine dubbed ELROTO and developed in the USA is based on U.S. Pat. No. 5,484,272 issued to Horn in 1996. While based on the much more suitable oscillatory rotating arrangement (also known as scissor action or cat-and-mouse design) this particular engine makes use of a drive mechanism based on overdrive cam arrangements that have a limited life span and do not lend themselves well to downsizing. The same is true of engine designs utilizing drives based on the use of ratchets (e.g. U.S. Pat. No. 5,400,754 issued to Blanco Palacios et al in 1995), or elliptical gears (e.g. U.S. Pat. No. 4,844,708 issued to Lopez in 1998).
An oscillatory rotating engine employs a plural number of rotors with interleaved vanes around the center of rotating. By changing the angular velocity of the rotors an oscillatory movement is superimposed on their uniform rotation, thus modifying the volume of the energy chambers defined by each pair of adjacent vanes and the inner surface of the engine housing. An inlet port, exhaust port and ignition device are provided at appropriate points on the housing, so that the expansion and contraction of the working chambers will provide induction, compression, expansion and exhaust strokes. The forces that alternately drive adjacent pistons apart or together are transformed through a motion transforming mechanism into forces that drive the output shaft.
A popular arrangement of the oscillatory rotating engines makes use of a planet gear and crank drive mechanism, such type of drive employed in the engine of my U.S. patent application Ser. No. 09/523,774, filed Mar. 11, 2000. While inherently more robust, this type of drive cannot scale down sufficiently to meet the requirements of the target applications of this patent application.
At least two prior art patents disclose designs that could potentially scale down sufficiently to drive small appliances.
One is U.S. Pat. No. 4,553,503 issued to Cena in 1985, disclosing an oscillatory engine with a drive mechanism utilizing eccentric cranks linked to and driven by an eccentric ring. While the underlying approach is promising, the design particulars are such that only two strokes occur per each revolution of the output shaft, thus reducing the unit power and necessitating the complexity of a forced phasing mechanism.
The other is U.S. Pat. No. 4,053,111 issued to Cronen in 1997, disclosing a toroidal engine with a drive mechanism comprising a crank shaft, eccentric pivot arms and a four-bar linkage. While quite elegantly designed, a scaled down version of this mechanism would not ensure the needed degree of simplicity or reliability for the target applications.
It is therefore a principal object of this invention to provide a rotary piston engine that would meet the design criteria specified herein while avoiding the pitfalls listed above.